1. Field of the Invention
The invention is related to turbo-prop engines and in particular to a propeller brake for a twin-spool turbo prop engine.
2. Prior Art
Propeller brakes for conventional piston engines and turbo-prop engines are known in the art. These brakes however are designed to stop the rotation of the propeller in the event of an engine failure, first to reduce the aerodynamic drag of the windmilling propeller in flight, and secondly to prevent further damage to the engine by the continued rotation of the propeller. Quick in U.S. Pat. No. 2,141,091 discloses a friction brake for the propeller of a piston engine. Bain in U.S. Pat. No. 2,737,018 discloses a friction brake for a turbo-prop engine which is actuated in response to a reduction in the oil pressure in either the engine or reduction gearing assembly when the engine is shut down. The brake is released by air pressure when the engine is being started. Alternatively, Dison in U.S. Pat. No. 3,225,876 discloses a propeller coupling for a turbo-prop engine which disengages the propeller from the turbine engine whenever the rotational speed of the propeller exceeds the speed of the engine by a predetermined amount.
It is often desirable to stop the rotation of the propeller of a turbo-prop engine for other reasons, in addition to stopping the rotation of the propeller in the event of an engine failure.
Presently it is required to stop the engine of a commercial turbo-prop powered aircraft when passengers are boarding or leaving the plane. The thermo cycling of the engine occasioned by the frequent starting and stopping of the engine at each stop appreciably reduces the life of the engine. The stopping of the engine further requires the use of an auxilliary power unit to provide the essential electrical and hydraulic services to the aircraft during the period when the engine or engines are shut down.
From an efficiency point of view, it is desirable keep the engines running while the passengers are boarding or leaving the plane. However the rotating propellers are highly dangerous to unwary passengers and crew members in the immediate vicinity of the aircraft. Additionally, even in their feathered state, the whirling propellers produce objectionable wind gusts.
The disclosed invention is a propeller brake which is a solution to this problem.